2003 4.0 Ranger problems...

[Kentuckybourbon]

Hey, im new to the forums and tried searching prior posts to see if could get some help with my problem but i didnt see anything.

I have an 2003 4X4 Ranger with 43k and im having some issues.


Whenever i turn my heat and or ac on and the truck is sitting at idle, it seems to want to surge forward. Almost like something is fighting to turn on or off, i can feel and see the whole truck jolt forward. it will do this every 5 or ten seconds. As soon as i turn off the fan the problem goes away. I looked under the hood and it looks like the ac pulley stops and starts periodically(is that normal?) but im not sure if that is the problem.

Could it be a vacuum leak? about a month ago my check engine light came on and i noticed the metal hose that plugs into the rubber boot by the mass air sensor was unplugged, i put that back in, unplugged the batter and the check engine light went away.....but now the issue above started happening..

any help would be appreciated....

 

[dorman68]

I think what is happening is that when you have your ac or heater on the compressor cycles on and off and when this happens the pcm raises the idle to compensate for the load the compressor puts on the engine. My wife's Toyota does the same thing.

 

[Kentuckybourbon]

I think what is happening is that when you have your ac or heater on the compressor cycles on and off and when this happens the pcm raises the idle to compensate for the load the compressor puts on the engine. My wife's Toyota does the same thing.

If this is the problem, is there anyway to fix this?

 

[jmg8550]

Not really. It's all controlled by the PCM. dorman68 is right. The extra load placed on the engine causes idle surge. does your RPM go up considerably? or is it just a slight bump.

 

[Big Jim M]

The surging is caused by the A/C compressor coming on and off again. In the HEAT position the compressor should NOT come on. However in the DEFROST position the compressor does come on..
Big JIm

 

[Kentuckybourbon]

Not really. It's all controlled by the PCM. dorman68 is right. The extra load placed on the engine causes idle surge. does your RPM go up considerably? or is it just a slight bump.

Idle doesnt really go up, the truck just surges and jolts forward.

 

[Kentuckybourbon]

The surging is caused by the A/C compressor coming on and off again. In the HEAT position the compressor should NOT come on. However in the DEFROST position the compressor does come on..
Big JIm

This might sound dumb but how can i tell the difference between heat and the defrost. Looking at my settings i just see the blue and red knob and the other knob has settings on which vent the heat comes out....